Large diameter fiber optics, often referred to as "flexible light pipes", are well known in the art, and typically comprise a single, solid core fiber which is surrounded by a cladding layer and a sheath or shielding layer. The core is the portion of a light pipe which transmits light, and typically has a diameter of about 2 to 12 mm. It is formed of a very soft, semi-liquid plastic material, such as OPTIFLEX.RTM., which is manufactured by Rohm & Haas Corporation, of Philadelphia, Pa. The cladding layer typically comprises polytetrafluoroethylene (PTFE or TEFLON.RTM.), or the like, while the outer sheath is fabricated of a material such as polyvinylchloride (PVC). Unlike small diameter optical fibers, which are typically used to transmit information in relatively complex control systems, these large diameter "light pipes" are typically employed in a variety of illumination systems where direct lighting is difficult to maintain, dangerous, or subject to vandalism. Examples include architectural lighting, display cases, pools and spas (to eliminate electrical connections near water), hazardous material zones (to eliminate the need for sealed lighting), or jail cells. They are particularly advantageous in that only a single centralized illumination system must be maintained, rather than a plurality of individual lights.
There are problems, however, in implementing state of the art light pipe illumination systems became of the difficulty of illuminating a plurality of light pipes from a single illumination source. In order to maximize efficiency, the optical fibers must be bundled as closely as possible, to ensure the maximum ratio of core area (the part of each light pipe which actually transmits light) to total area. However, bundling the large diameter light pipes together in order to illuminate them from the single illumination source is difficult to do efficiently. Each of the individual light pipes are round and thus have a great deal of space between them due to the cladding and shielding layers. This problem is illustrated in prior art FIG. 1, wherein a bundle 2 of large diameter optical fibers or light pipes 4 is shown. Each optical fiber 4 comprises a core 6, a cladding layer 7, and a shielding layer or sheath 8, as described above. To obtain maximum efficiency, it is desirable to illuminate only the core 6 of each of the bundled optical fibers 4, but this is impossible using state of the art bundling techniques. Necessarily, if the light from the source of illumination is spread across the array of optical fibers, it will illuminate not only the cores 6 of the optical fibers 4, but also the cladding layers 7 and the shielding layers 8. Furthermore, the voids 9 between the optical fibers, which are inevitable because of the fibers' round dimensions, also are impacted by the light from the illumination source. All of the light falling upon any element other than the cores 6 is wasted, and becomes an efficiency loss, since it will not be transmitted by the fibers. Additionally, packing the fibers so closely together creates problems such as mechanical difficulties in configuring and accommodating the illumination system and difficulties encountered in attempting to replace one of the individual bundled fibers. This design also typically results in color variation between fibers unless techniques are specifically employed to prevent this problem.
One prior art solution to this problem has been to eliminate the sheathing and cladding layers about each optical fiber, in order to reduce the area across the bundled array of fibers which does not transmit light. However, there is still a packing factor problem because the optical fibers are round, and there are other physical disadvantages in eliminating those layers. Thus, this solution is unsatisfactory for most applications.
What is needed, therefore, is an illumination system which more precisely illuminates only the core of each light pipe, in order to maximize efficiency by preventing light losses. Such a system would also preferably permit the use of spaced, rather than bundled, optical fibers. This is because the whole image of the arc of the lamp is received by each individual fiber, rather than collectively on a bundle of fibers so that each fiber receives a different part of the arc. Spacing the fibers also would assist in maximizing the flexibility and adaptability of the illumination system in terms of application to different environments.